Fractionation of clay



July 15, 1941. G. J. LANE E'rAl.

FRACTIONATION 0F CLA-Y Filed July 29, 1940 marea my, is, 1941 UNITEDASTATES PATENT oFFlcr:

2,249,570 raac'rroNArroN or CLAY George J. lane, Metallen, N. I.. andDonald 8.

Phelps. Harvard, Mall.,

alalgnorato Edgar Brothers Company, Metuclien, N. J.,a corporation ofNew Jersey l Application July 2.9, 1.940, Serial No. 348,174

s clam (ci. zoo- 166) Fractionation of-clay by particle size isdesirable for various purposes, and yis of particular advantage in theproduction of clay for the paper industry, e. g., not only clay to beused as filler, but especially clays to be used in coating compositions,notably in the manufacture of coated papers to have a high smoothness orgloss.

For example, a crude white clay which is mined at McIntyre, WilkinsonCounty. Georgia, and

which essentially comprises clay or kaolin' of satisfactory quality forpaper use, has a clayparticle size range from 40 to 50 microns inequivalent spherical diameter, down to a fraction of a micron. By farthe major content is in par-h ticle sizes of not more than about 20 to25 miicrons, and it is within this conter/it that fractionq ation toobtain products of liner particle size is ordinarily desired; the largerclay particles being either inconsequential or susceptible of reductionby grinding, or being eliminated in p'art by the cleaning treatmentsemployed to remove contaminating particles, such as mica, sand,ilmenlte,

tourmaline, particles of iron compounds, and clay particlessubstantially contaminated -with compounds of iron or titanium. Inreference to particle size, it will be understood by those skilled inthe art that the equivalent spherical diameter of a clay particle is thediameter as calculated from sedimentation measurements, which diameterhas been proven to approximate very closely the mean of all diameters,in various directions, of the actualy particle.

As an instance of fractionated products, one

Aclay fraction contains not more than 2% in particle size larger thanabout three and one-half microns and is substantially free of materialcoarser' than 4 or 5 microns. This product, made by the same company andcalled Satin, is a very fine quality coating clay, susceptible of beingcalendered to an 4extremely high smoothness and gloss. It will beunderstood that each-of these fractions contains lsubstantial quantitiesof particles smaller than the stated maximum, and indeed ranging down tofractions of a micron. It may'also be'explained that when the' cleanedor purified clay is treated to produce these products consistingmostlyof particle sizes from 20 or 25 microns down to or 5, 'also constitute asalable product for the paper trade,l particularly for lling.

Heretofore, the procedure for washing and cleaning the clay, andparticularly the fractionating procedure, has usually involved extensiveand relatively costly operations. 4The apparatus includes not only trapsand settling troughs for :10 sandand other impurities, but forfractionation,

equipment such as specially designed centrifugal machines, mills, andlarge sedimentation basins;

and special de-flocculating treatments have been required in connectionwith centrifuging and sedl5 imentation. It is accordingly an object ofthe present invention to provide improvements in clay processing,particularly forfractionating clay (i. e., as to particle size) with anotable ease of control, substantial economy and high emciency lofoperation, and with much simpler or less expensive apparatus, than has'generally been required heretofore. Another object is to provide asimplified procedure 'which may provide,V in a unied operation, both forcleaning or purifying the clay and for fractionating it to a desiredparticle size; further objects including such as are hereinafterstatedVor apparent or are incidental to the practice of the invention.

To these and other ends, it has now been dis-I covered that a clean andsatisfactory fractionationof clay, as to particle size and particularlyfor. the reduction of the content of the given clay in particles largerthan any predetermined size,

may be accomplished by froth flotation, e. g., treatment of the clayslip in the presence of suity able reagent material and in suitableaerating apparatus, to produce a frothvwhich selectively tends toelevate in the froth' the finer clay particles.

justed or made progressivel more effective for the liner clay particles;the ragility of the froth and other factors beingthus controlled, forinstance as hereinafter explained, for recovery ofa clay concentratewhich is substantially free'oi' material coarser than themagrimumparticle size desired.

According td -present understanding of the process, .advantage is takenof the affinity of suitable frothing reagent material, such as sul- (e.g., Satin and HT), t/he residue fractions. ftib1e ofready contraltoobtain adenite selec- Under the selected circumstances, the 40clay-elevating tendency of the froth may be adtivity toward particlesnot larger than any given size. Among the factors that may be regulatedto that end are the solids content of the feed, the amount of reagent,and time of rise or other travel of the froth from its origin totheplace. 5

tributed all over the surfacesl of the bubble-.l0

films, the ability of the froth Ito carry the clay" tends to vary in aninversel relation tothe particle size; and thus the action is notanalogous to the flotation separation of one material from a differentmaterial, i. `e.',vwhe1:e the particles of 15 theconcentrate differ inchemical composition or in physical structure or even in density, fromthose of the tailing. For instance,` the more fragile or the more mobilethe froth or thefurther it has to rise in a column before its overflowand collection', the; greater seems to be the tendency for largerparticles to break through or fall between the bubbles and thus:accumulate in the tailings. Extensive tests have also revealed that thecleanness of fractionation is in considerable measure dependent upon thenumber of successive flotation treatments. Thus for instance, withreagents of the character mentioned, it has been foimd desirable toemploy a series of three or four cells in order to obtain fine fractionscorresponding, say, to Satin" or HT grades, when the original feed issimply a, pulp of the crude clay.4 In other cases, however, aswherefractionation is ydesired of'an'already partly refined clay, one ortwo froth notations may suffice. 35

the solids content of the feed. In general, the 40 more dilute the p ulpat the feed end of a cell. the greater is the percentage of the nner orfinest particles in the concentrate with respect to the actualV amount of solids in the feed.

tion of concentrates having desired ilneness in any given operation, butthe tailings in a given setup may themselves amount to a fraction ofanother sort (for example, the residue fractions to further liketreatment for separation of im` purities (e. g., where'the originalmaterial was a crude clay) and even for. further fractionation ofrelatively coarse sizes if desired. As indicated above, moreover, theapplication of the`invention to crude claysv has the further advantagethat various contaminating particles, for `instance .those mentionedhereinabove, are removed dur- V ing fractionation, usually in the firstor secondfA the pulp. Thus, for example, good results have 55 been hadwith the Callow type of froth flotation cell, wherein the aeration isdirectly obtained by blowinga'ir through, and-subdividing it with, atine canvas screen beneath the pulp column.

Especially advantageous operation has been achieved with a cellproviding both direct aeration and self-agitation, and comprising aseries of ducts extending down into a central plup chamber for` blowingair into the pulp, and adjacent frothing chambers to which the agitatedand sented pulp mana in which a. rising froth column, advantageously ofsubstantial height. is produced to pass over into suitable collectinglaunders. It will be imderstpod that inl such cells the central chamberis preferably separated fromthe frothingchamber by'- depending baiilesextending down into and slightly below the l normal pulp surface, andthat upon the vigorous injection of air, the pump is not only aerated,

but effectively agitated as it circulates in the central chamber landthence to the frothing chambers. Substantiallysubmerged baiiles,clearing the bottom lof the cell, extend along each side of the series of airducts in the central chamber,`

to aii'ord circulation overv such bales and under the other bames, intothe froth chambers.

The drawing shows a schematic diagram of one system in` which theinvention has been employed, and certain specic examples of theinvention are hereinafter described, but it will be undrstoodthat these'procedures and apparatus" are set forth only by way of illustration andthat the invention *is susceptible of modification in many respects,which will be readilyl appreciated by those skilled in the' art. f v

By 'way of specific instance, the hereinabov described, untreated whiteclay froma mine at McIntyre, Georgi. Was subjected to the followingprocedure in the apparatus indicated in the drawing to obtain a unefraction equal to the above-described "HT" grade: The -clay was blungedwith water to `produce a slip containing about 25% solids, andv afterpassing the slip through sand-cone separators toremove coarsematerialsuch as coarse sand, gravel and the like, sulilte waste liquorwas incorporated in the pro' portion of about 25 pounds per ton of dryclay. In this run the sulilte waste liquor was one obtained from a woodpulp mill in Maine, and was derived from.. sulflte treatment of a blendof northern `spruce and northern hemlock: it appearing from other teststhat sulfite liquor from these woods has preferable qualities for thepurposes of the present invention. 'Ihe liquor had Not onlyistheprocedure applicable to producbeen somewhat evaporated, to have aspecific 10% pounds per gallon.

l After thorough mixing to obtain full permea tion lof the liquor in thecrude clay suspensionmentioned hereinabove) or may be subjected 50suchpenneation being apparently desirable to attain the optimum intimateaction on the clay in the-flotation treatment-the resulting slip or pulpwas fed 'to a flotation apparatus comprising four cells of the combinedagitation and .aeration type described hereinabove.` The four cells arediagrammatic'ally shown in the drawing: as

there set forth, the apparatus was conveniently so arranged as to feedthe froth concentrate from sulting refinedpulp from'the bottom of thetank.

to feed the next cell. The froth from cell No. l was collected, forrecovery therefrom of a highly refined clay; and the cells wereconnected in la closed circuit at thevtails ends, so that the onlytailings came from No. l cell. That is, the tailings of the fourth cellwere returned into the feed of the third, those of the third into thefeed of the second, andithose of the second into the feed of the rst,whereby the final concentrate consistedvof the collected froth of thefourth cell and the ilnal'tailings. were taken from and those o long. Asdetermined by the'height of the tail 15. Y gate, each cell'had a pulplevel or column about 424 inches high. and in the froth chambers a vthan about-15 microns. Paper coating test with v each cell.

the end fof cell No. i. Operation was had at the ning lengthwise on bothsides: each froth gate of theNo. i and No. 2 cells was about eight feetlong, those of the No. 3 cell about four feet long f No. I ,about threefeet. six inches froth column about 30 inches high. to the edge of thefroth gate. Air 'was supplied through a multiplicity of one-half inchwise on about 3inch centers and extending vertically down to a pointnear the bottom of the aeratlng chamber, as explained above.

The run specifically described above was carried on continuously for 31hours, feed of 33 tons of crude clay (dry weight) and the concentrateyield was about 75%.. The concentrate, which was the froth concentratefrom the No. 4 cell, was lcollected in the collecting each hadfroth-collecting gates and launders run- 10 Pipes spaced length- 20 witha total 25 about 4%%: but the thus fractioned product was finer than'inthe previous runs. The same paper coating test of a representativelsample produced a smoothness, uncalendered, of 23 seconds, representinga product considerably liner than HT and not a great deal coarser thanthe finest or Satin" grade hereinabove identified.

Other tests,.particularly for coating smoothness and "gloss, coniirmedthe above-stated determinations of the results of these runs. and liketests made on samples taken from the tailings and from the concentratesof intermediate cells in the system as operated, showed that thefractionation was selective in accordance with the number of cellsused-i. e., the product becomes increasingly liner in maximum particlesize, with the number of times it is subjected to the flotationoperation.

It will be understood that the tailings from operations of theinvention, for example those described above. may be subjected tofurther flotation not only for cleaning (to obtain a relatively coarsethough useful fracton) but for further fractionation in some cases--forinstance in the case of thel run last above set forth, to

obtain any intermediate fraction somewhat Aooarser than the HT grade butmeasurably l finer than the ordinary cleaned clay.

tank and was `found to contain about 23% solids. 30

Examination and tests of the concentrate. showed it to consist of a lineclay fraction of very good "HT" quality. That is, the thus fractionatedproduct was not only free of any appreciablev content of contaminatingparticles. but consisted of substantially pure kaolin containing notmore 'particle size, and substantially no particles larger Other runswere m'ade'with the same appara- -than about 1% larger than 12 or 1.3microns ini tus. and comparable or better 'results obtained.,

Thus in one such Aother run. the feed was di-y luted to about 14% solidsand was effected at a 5 rate of about 3A of a ton of crude clay perhour. The concentrate' from' the No.. l cell contained about 5% solidsand represented a yield of about The changed conditions aiorded afurther or nner fractionation: in this instance, the same paper coatingtest on the product showed a smoothness, uncalendered, of about seconds.In a still further run with the same appara" tus, the dilution-and rateof feed to No. i cellwere the same as in the lastmentioned instance: ,6the reagent being in the same proportions n this as well as both of therabove runs, viz., 5 pounds of the sulilte waste liquor per ton of crudeclay. In this further run, however, further dilution was effected byadding clear water 6 into the feed end'of No. l cell, in an amount notquite equal in volume to the pulp feed'to It will also be understoodthat the fractionated product of the invention-e. g., the concentratefrom the systemvillustrated-may be .subjected to the usual bleachingprocedure where the inherent colors of the clay is darker than desired,and for use or shipment may be coilected by 'filtration and dried, inthe usual mannen The fractionating procedure of the intention has alsobeen successfully carried out with the Callowt type of flotationv cell.Numerous -runs have been made with such equipment and equally goodfractionation obtained. In one representa.-

tive-run, the original feed (crude clay) contained solids andthefractionating reagent was sulte waste liquor incorporated in the feed inthe proportion of pounds per ton of crude clay. The clay was refloatedthrough the Callow cell 3 times, using only the previous concentrate foreach operation after the first, and discarding 'all tails. Dilution wasprogressively increased in 0 the successive` feeds. so that in y thelast flotation D the thus fractionated product, including the papercoating test, which yielded `an luncalendered smoothness of 48 seconds,demonstrated tamed about 3%. sonas and @nordest yield of 75 its fullequivalence to the -Satin" grade, containing practically no particleslarger than three to three and one-half microns.

The Callow cell appears to yield a more fragile froth, and thus asomewhat increased selectivity' toward the finer particles, than thecells in.

which the aeration is accompanied by consider- 0r able agitation, but ahigher recovery (e. g., in

dealing with any given-fraction other. perhaps, than the very nnest) hasbeencbtained with cells of the latter type.

' As stated. an example of a suitable reagent is sulflte waste liquor,and although other sulte -35 pounds per ton of clay treated, it has beenfound that the toughness of the froth increases to some extent with theamount of the reagent,

' other than 'the illustrative examples set forth e. g., suli'ite wasteliquor or equivalent material having like action. By the same token,change in the solids content of the feed, with the proportion of reagentto dry solid constant, tends to alter the froth; the more dilute thefeed, the more fragile the froth and thus in general, the greater itsselectivity for the finest particles;

Certain further factors, as explained above, may be collectivelyexpressed as the time of rise of the froth column, e. g., the averagetime consumed as the bubbles travel from the pulp to the top of thefroth gate over which they ilow into the launder; generally speaking,the longer the time of rise, the greater the particle size selectivity.It appears that as'the froth travels up in the column, a partialbreakdown is constantly going on,fpermltting more and more of the largeparticles, and greater numbers of particles yof intermediate size, tofall /back into the pulp. The time of froth rise isbdependent upon .theheight of -the froth gate above the tails gate, upon-the amount of airflow into the cell (theA greater the flow, the faster the rise), and t5some extent by the solids content of the pulp,it being generallyobserved that the greater the solids content of the pulp (other thingsbeing equal) the faster the rise of the froth column. For example, inthe nrst example yset forth hereinabove, in the production of HT gradeof clay, the average time of froth rise appeared to be about to 20seconds, i. e., about seconds in cell No. 4, and progressively less inthe earlier cells, down to 15 seconds or some-l what less in cell No. 1.On the other hand, in

operating with the Callow cell in making Satin clay, the froth rise inthe final flotation consumed at least about a minute, and times of` theorder o f 30 seconds or morel inthe earlier notations.

Although for simplicity of explanation and for ease of determination inmaking tests (analysis of concentrates being most conveniently made bycomparison with `known standards of clay) the foregoing description hasbeen chiey related to the specific grades of clays named, it will beunderstood that the procedure is susceptible -of producing any of agreat variety of clay fractions, simply by suitable regulation of thecontrolling factors as will now be readily understood by those skilledin the art.

- Indeed, in view of what has now been ex# plained, the successfulapplicationv of the invention to produce a desired clay fraction underany given circumstances is a matter of appro- Drlate design orregulation of controlling factors' such as the solids content of feed,the amount of reagent, the height of the froth column, the extent ofaeration and vagitation and the number of successive notations. Itlsmanifestly unnecessary here to specify .the exact values. of thesefactors which will be best `in above. The principles of the inventionhaving been explained, the optimum conditions to obtain a clay ticlesize from .any given starting material (be it crude clay, cleaned clay or the concgmtrate or tailing from a previous fractionation) can bereadily and rapidly ascertained without extensive experiment but bysimple adjustments-or tests in accordance with the above-noted effectsof the several factors-all as will now be understood by those familiarwith the prerequisites to setting up Aa successful flotation plan,embodying any ordinary or previously known concentration process.

The various` smoothness determinations on coated Dfper were made, asstated. with the Wil- -liams smoothness tester, a standard and widelyused device for such purpose. In this apparatus, the coated sheet undertest is centrally perforated and placed on a circular platform which hasa central air e and a gum rubber facing for sealing surface to be testedfaces up and a plane surfaced glass disc is pressed down against it. Theair e in the platform (leading to the aperture in the paper) connectswith a pump and with a chamber for controlling amercury column; thelatter being initially adjusted to a xed low level. The pump pistonis'then forced down, compressing the air in the chamberV and raisingrthe mercury to an electric contact, lwhich `sets oil!l an electricclock. 'Ihe compressed air nowfilows out between the' paper and theglass disc, while the clock-runs, and when the mercury drops to a secondelectrical contact at a predetermined low level, the clock is turnedolf. The'time is thus automatically measured for the flow of a fixedvolume of airout between the ycoatedA surface andithe glass disc; thesmoothness readings thus being in secondsthe higher the smoothness, thelonger the Vtime of air ilow. l

i It will be understoodthat the invention is not limited to theprocedures hereinillustrated and described, but may be extendedvto oremploy equivalents, and may be carried outmother ways,v withoutdeparture from its spirit.

. What isclaimed is: t

1. In a method of treating clayrmaterial to fractionate the same inparticlesize to obtain a clay .fraction having a maximum particle sizewhich is smalle than 20 microns, and wherein the clay. material includesa substantial content-of clay panticles at least as '20 microns'andlarger than the desired fraction, o f the clay material and subjectingthe same to froth flotation `treatment in the'presen'ce of sulilte wasteliquor, including aeratlng the pulp to produce a moving, clay-carryingfmthvand collecting the froth at the end of its travel, whilemaintaining a sumciently low solids content in the pulp. sui'ilcientfragility`of frothbubbles and Vsuillcient time of travel fof the froth,in correlam'axirnum of the tion to inhibit supportby the collectedfrothof aforesaid maxiclay particles larger than the mum.'

,r 2. In a method -of treating-.clay material to fractionate the same inparticle size to obtain a clay fraction having a maximum particle sizewhich is smaller than 20 microns, `and wherein the Nclay materialincludes a.substantial content o'f clay particles at least as as aboutfraction of a desired fineness of parcontact with the paper. The

small as about the steps ofestablishing a pulp 20 microns and largerthan lthe maximum of the desired fraction, the steps of establishing apulp of the clay material containing sulfite Waste liquor, aerating thepulp to produce a rising column of froth and collecting the froth fromthe top of the column, while coordinating and maintaining at asufficiently high value the fragility of the froth and its time of riseto inhibit the support, in the froth concentrate, of clay particleslarger than the aforesaid maximum.

3. In a method of treating clay material to fractionate the same inparticle size to obtain a clay fraction having a maximum particle sizewhichis smaller than 20 microns, and wherein the clay material includesa substantial content of clay particles at least as small as about 20microns and larger than the maximum of the desired fraction, the stepsof establishing a pulp of the clay containing sulte waste liquor;subjecting the pulp lto flotation treatment for production of a rising,clay-carrying froth column, said notation treatment including aeratingthe pulp with the factors of the solids content of the pulp and theconcentration of sulflte waste liquor therein maintained sumciently low,the rate of aeration sufhciently slow and the height of the froth columnsuiliciently high, in correlation, to produce a froth havingclay-elevating power substantially selective toward particles not largerthan the aforesaid maximum; and collecting the elevated froth.

4. In a method of treating clay material to fractionate the same inparticle size to obtain a clay fraction having a maximum particle sizewhich is smaller than 20 microns, and wherein the clay material includesa substantial content of clay particles at least as small as about 20microns and larger than the maximum of the desired fraction, the stepsof establishing a pulp of the clay material and subjecting the same torepeated froth flotations in the presence of sulte waste liquor, whilemaintaining sumcient fragility of the froth in each flotation operationand performing a suilicient number of said successive operations incorrelation to produce in each operation a froth having clay-elevatingselectivity for particles not larger than the maximum, and to produce afinal froth concentrate trate, and separating the resulting ne fractionof clay therefrom.

5. A method of fractionating clay marterial which contains a substantialcontent of clay particles at least as small as about 20 microns andlarger than the desired fraction, to obtain a clay fraction of notlarger than a predetermined fine particle size, said predeterminedparticle size being a size smaller than 20 microns, comprisingsubjecting a pulp of the clay to a plurality of successive frothi'lotations in the presence of suliite waste liquor, while maintainingthe factors of the solids content of feed and the amount of sulfitewaste liquor suillciently low, the height of froth columns sufficientlygreatand the extent of aeration sufficiently small, in correlation Witheach other and with a suiilcient number of successive notations, toproduce a final froth concentrate substantially free of clay particleslarger than the aforesaid predetermined size.

6. In a method of treating clay material to fractionate the sameinparticle size to obtain a clay fraction having a maximum particle sizewhich is smaller than 20 microns, and wherein the clay material includesa substantial content of clay particles at least as small as about 2Omicrons and larger than the maximum of the desired fraction, the stepsof establishing a pulp of the clay material, and subjecting the pulp tofroth flotation operation in the presence of sulte waste liquor, saidflotation operation including aerating and agitating the pulp to producea rising froth column, with the factors 0f solids content of feed andthe concentration of sulflte waste liquor maintained suiiiciently low,the height of the froth column sufliciently great, and the extent ofaeration and agitation sufllciently small, in corelation, to produce afroth having a fragility and time of rise adapted to reject clayparticles larger than the aforesaid maximum, and collecting the frothfrom the top of its column.

GEORGE J. LANE. DONALD S. PHELPS.

